The present invention relates in general to the art of earth boring and more particularly to a cutting element for an earth boring apparatus.
Earth boring apparatus having hard insert elements mounted in a cutter member body are utilized in the boring of holes in the earth because of the ability of the hard insert cutting elements to penetrate the earth formations. A problem has been encountered with this type of apparatus, and generally with all earth boring apparatus, in maintaining the desired diameter or gage of the hole being bored. This is important in the boring of raise holes and tunnels as well as being critically important in the drilling of oil and gas wells and the like. For example, in the drilling of a deep well wherein more than one bit will be used in the well, the gage cutting inserts must maintain the hole at the full diameter. Otherwise, it would be necessary for the next bit being lowered into the hole to ream the undersized hole out to the desired diameter before the new bit reached drilling depth and could begin drilling its length of assigned hole. Such reaming action would reduce the useful lifetime of the second bit because by the time the second bit reached its assigned drilling depth, a substantial part of the lifetime of the gage cutting elements would be exhausted.
The inserts in the gage row are exposed to the most rigorous drilling. They must drill a larger area of the hole. In addition, the formation outwardly of the gage row of inserts is not being drilled and hence provides some degree of lateral support for the formation being drilled by the gage row. It will be appreciated that an improvement in the ability of an earth boring apparatus to maintain gage will be an improvement of the entire earth boring apparatus and contribute significantly to the performance efficiency, economy, and life of the earth boring apparatus.